1. Field of the Invention
This invention relates to mold box retaining means and especially to mold box retaining assemblies for use in hydraulic presses which compress powdered ceramic materials or the like.
2. Prior Art
In the mechanical or hydraulic press art, there usually is a mold case to which a mold box is secured. The mold box has a central cavity into which the top die or plunger and the bottom die or plunger moves and which cooperates therewith to form under high pressure a tile or brick. The mold box took various forms. One common form had four parts, a fixed rear beam, a front beam, and two intermediate transverse side beams with bolts passing inwardly through the front and rear beams to threaded passageways in the side beams. Some of the outer walls of the beams had projecting keys which mated with corresponding channels in the mold case. Such keys, of course, required considerable machining. Furthermore, by the nature of their construction, removal of at least one of the beams was required to enable the lower die to be inserted horizontally. Removal of the beam or beams required removal of numerous bolts which was not only time-consuming but also difficult and awkward. When such mold boxes were assembled to the mold case and subjected to extremely high pressures by the downward movement of the upper ram-die assembly, the intense vertical pressure acting upon the powdered material in the mold cavity produced a correspondingly intense outward pressure exerted on the inner walls of the mold box. The pressure was such as to cause those inner walls to be pushed outwardly and to deform the bolts resulting in the loss of the requisite geometric integrity in the mold cavity for production of first-grade tiles or bricks or the like. When this happened, the necessary small tolerances in the mold cavity could not be maintained and the useful life of the mold box was considerably shortened. So-called "fins" appeared on the pressed product caused by the yielding walls of the mold box and these fins were not commercially acceptable. If the actual mold box cavity tolerances departed unacceptably from the desired tolerances, the mold box would become mutilated and unusable and the fabrication of new mold boxes would require considerable additional expense.
Other approaches to fastening a mold box in a mold case have involved the use of a special plate with a number of discontinuities which are curved and with which a corresponding number of curved wedges are used. Such a structure is shown in U.S. Pat. No. 3,447,205. It is clear that that is a highly complex assembly which requires extensive machining or special forming and, in any event, also has a mold box-wedge relation which requires the use of a key.
It is therefore among the objects of the present invention to provide a novel wedging assembly for fastening mold boxes or the like in a key-less frictional arrangement, which permits vertical withdrawal of the mold box in a much more accessible, time-saving fashion.